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FreeBSD-SA-16:30.portsnap                                   Security Advisory
                                                          The FreeBSD Project

Topic:          Multiple portsnap vulnerabilities

Category:       core
Module:         portsnap
Announced:      2016-10-10
Affects:        All supported versions of FreeBSD.
Corrected:      2016-09-28 21:33:35 UTC (stable/11, 11.0-STABLE)
                2016-09-28 22:04:07 UTC (releng/11.0, 11.0-RELEASE-p1)
                2016-10-05 00:33:06 UTC (stable/10, 10.3-STABLE)
                2016-10-10 07:18:54 UTC (releng/10.3, 10.3-RELEASE-p10)
                2016-10-10 07:18:54 UTC (releng/10.2, 10.2-RELEASE-p23)
                2016-10-10 07:18:54 UTC (releng/10.1, 10.1-RELEASE-p40)
                2016-10-05 01:01:10 UTC (stable/9, 9.3-STABLE)
                2016-10-10 07:19:16 UTC (releng/9.3, 9.3-RELEASE-p48)

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

The portsnap utility is used to fetch and update compressed snapshots of
the FreeBSD ports tree. Portsnap fetches snapshots and updates over http,
and then cryptographically verifies the downloaded files.

II.  Problem Description

Flaws in portsnap's verification of downloaded tar files allows additional
files to be included without causing the verification to fail. Portsnap may
then use or execute these files.

III. Impact

An attacker who can conduct man in the middle attack on the network at the
time when portsnap is run can cause portsnap to execute arbitrary commands
under the credentials of the user who runs portsnap, typically root.

IV.  Workaround

The ports tree may be obtained by methods other than portsnap, as
described in the FreeBSD handbook.

V.   Solution

portsnap has been modified to explicitly validate compressed files within
the tar file by full name, rather than relying on gunzip's filename search
logic. portsnap now verifies that snapshots contain only the expected files.

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

No reboot is needed.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility.

This advisory is released concurrently with FreeBSD-SA-16:29.bspatch
which contains special instructions for using freebsd-update. Following
the instructions in that advisory will safely apply updates for
FreeBSD-SA-16:29.bspatch, FreeBSD-SA-16:30.portsnap, and
FreeBSD-SA-16:31.libarchive.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 10.x]
# fetch https://security.FreeBSD.org/patches/SA-16:30/portsnap-10.patch
# fetch https://security.FreeBSD.org/patches/SA-16:30/portsnap-10.patch.asc
# gpg --verify portsnap-10.patch.asc

[FreeBSD 9.3]
# fetch https://security.FreeBSD.org/patches/SA-16:30/portsnap-9.3.patch
# fetch https://security.FreeBSD.org/patches/SA-16:30/portsnap-9.3.patch.asc
# gpg --verify portsnap-9.3.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r306701
releng/9.3/                                                       r306942
stable/10/                                                        r306697
releng/10.1/                                                      r306941
releng/10.2/                                                      r306941
releng/10.3/                                                      r306941
stable/11/                                                        r306418
releng/11.0/                                                      r306419
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://gist.github.com/anonymous/e48209b03f1dd9625a992717e7b89c4f>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:30.portsnap.asc>
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